Holding device of recording medium, image forming apparatus, and conveying method of recording medium

ABSTRACT

According to one embodiment, the image forming apparatus includes, an endless device having a plurality of suction holes, and a negative pressure chamber which communicates with the suction holes, a rotation mechanism which rotates the endless device, a suction mechanism which discharges air in the negative pressure chamber, an opening and closing mechanism which has a switching blade which opens and closes the suction holes, a driving mechanism which moves the switching blade to a first position and a second position, a recording head unit, a supply mechanism which supplies the recording medium to the endless device, and a controller. If the switching blade moves to the first position, the suction holes are shut. If the switching blade moves to the second position, the suction holes communicate with the negative pressure chamber. The controller drives the opening and closing mechanism according to the size of the recording medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from: U.S. Provisional Application No. 61/384,074 filed on Sep. 17, 2010, the entire contents of each of which are incorporated herein reference.

FIELD

Embodiments described herein relate generally to a holding device which holds a recording medium such as a sheet, an image forming apparatus, and a conveying method of the recording medium.

BACKGROUND

For example, an inkjet recording apparatus or the like, includes an endless device which is formed of a rotating drum or belt, and recording heads which are arranged along a circumferential surface of the endless device. The sheet is conveyed to the recording heads, when the sheet is held on the circumferential surface of the endless device and the endless device rotates. One example of the endless device is a drum whose circumferential surface is provided with a plurality of suction holes. In the interior of the drum, a negative pressure chamber which communicates with the suction holes, is defined. A suction fan is communicated with the negative pressure chamber. It is possible to adsorb the sheet onto the circumferential surface of the drum, since the negative pressure chamber has a negative pressure when the suction fan is rotated and air in the negative pressure chamber is discharged.

A holding device in the related art, which includes the endless device, has a plurality of negative pressure chambers which are formed by division of the drum in a circumferential direction of the drum. These negative pressure chambers communicate with a plurality of suction holes which are formed on the circumferential surface of the drum. Shutters which open and close each of negative pressure chambers are respectively provided to an end surface of the drum. When the shutter is open, the air in the negative pressure chamber with the shutter is sucked due to the suction fan, thereby generating the negative pressure in the negative pressure chamber. A sheet of a desired size is adsorbed onto the circumferential surface of the drum by generating the negative pressure in one or more negative pressure chambers, according to the size of the sheet. However, the holding device having the shutter in the related art is negatively affected by a shock which is transmitted to the drum when the shutter opens and closes, resulting in a poor image formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view which schematically shows the inside of an image forming apparatus according to a first embodiment;

FIG. 2 is a cross-sectional view which shows a sheet holding device of the image forming apparatus;

FIGS. 3A, 3B, and 3C are respective expanded views which show a circumferential surface of a drum according to the first embodiment and sheets of different size from each other;

FIG. 4 is a cross-sectional view which shows a part of the drum, and a switching blade at a first position;

FIG. 5 is a cross-sectional view which shows a part of the drum, and a state in which the switching blade moves to a second position;

FIG. 6 is a block diagram which shows a configuration of a controller of the image forming apparatus;

FIG. 7 is a flowchart which shows an image forming process of the image forming apparatus;

FIGS. 8A, 8B, and 8C are respective expanded views which show the circumferential surface of the drum according to a second embodiment and sheets of different size from each other; and

FIG. 9 is a side view which schematically shows the image forming apparatus according to a third embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, the image forming apparatus includes an endless device, and a rotation mechanism which rotates the endless device in a predetermined direction. The endless device includes a plurality of suction holes which are formed on the circumferential surface thereof, and a negative pressure chamber which communicates with the suction holes. Further, the image forming apparatus includes a suction mechanism which discharges air in the negative pressure chamber, an opening and closing mechanism which has a switching blade, a driving mechanism which moves the switching blade to a first position and a second position, a recording head unit, a supply mechanism which supplies a recording medium toward the circumferential surface of the endless device, and a controller. If the switching blade moves to the first position, the suction hole is blocked. If the switching blade moves to the second position, the suction hole communicates with the negative pressure chamber. The controller drives the opening and closing mechanism according to the size of the recording medium.

Hereinafter, the image forming apparatus according to the first embodiment will be described with reference to drawings FIGS. 1 to 7. FIG. 1 shows an inkjet printer 10 which is an example of the image forming apparatus. The inkjet printer 10 (hereinafter referred to as a printer) includes a housing 11, a drum 12 which is an example of the endless device which is accommodated in the housing 11, a sheet receiving unit 13, a supply mechanism 14, a charging roller 15, a recording head unit 16, a neutralizing charger 17, a sheet discharge mechanism 18, an operation unit 19 having a display device 19 a, a controller 20, a power switch 21, and the like.

The drum 12 which is an example of the endless device includes a cylinder portion 12 a, and rotates at a predetermined circumferential speed around a rotation axis 25 in the direction which is shown by an arrow R1, using a rotation mechanism which includes a motor 22 (shown in FIG. 6). The position of the drum 12 in the rotation direction is detected by a rotation angle sensor 26 such as an encoder, or the like. The cylinder portion 12 a of the drum 12 is formed of a conductive material such as an aluminum alloy, or the like. The cylinder portion 12 a of the drum 12 has an inner circumferential surface 12 b, and an outer circumferential surface 12 c. A dielectric layer 27 formed of, for example, a resin film is provided at the outer circumferential surface 12 c. The cylinder portion 12 a is grounded. A potential of the cylinder portion 12 a is maintained to 0 V as a counter electrode when being charged using the charging roller 15.

The sheet receiving unit 13 receives a plurality of sheets S as the recording medium. An example of the sheet S is a sheet of a regular size, and a resin film, or a label may be used. The supply mechanism 14 includes a pick-up roller 28, a sheet feeding roller 29, a separation roller 30, a sheet conveying path 31, and a pair of resist rollers 32. The sheet S, which is taken out one by one using the pair of resist rollers 32, is sent to the sheet conveying path 31. The leading end of the sheet S which is sent to the sheet conveying path 31, is aligned using the pair of resist rollers 32.

The charging roller 15 is provided to face the circumferential surface 12 c of the drum 12. A DC power circuit 34 is connected to the charging roller 15. When a DC voltage is applied to the charging roller 15 using the DC power circuit 34, a charge for electrostatically adsorbing the sheet S is generated on the circumferential surface 12 c of the drum 12. The sheet S which is adsorbed onto the drum 12 is conveyed toward the recording head unit 16. The charging roller 15, the dielectric layer 27 of the drum 12, the DC power circuit 34, or the like, forms an electrostatic adsorption device for electrostatically adsorbing the sheet S to the circumferential surface 12 c of the drum 12.

The sheet discharge mechanism 18 includes a separation member 35, a conveying guide 36, sheet discharge rollers 37, and a sheet discharge tray 38. A cleaner 39 for cleaning the circumferential surface 12 c of the drum 12 is provided between the separation member 35 and the charging roller 15. The charging roller 15, the separation member 35, and the cleaner 39 include a moving mechanism for being separated from the sheet S, in order not to come into contact with a surface on which an image of the sheet S is formed, when the sheet S passes through after the image formation.

The recording head unit 16 includes inkjet head 16 a, 16 b, 16 c, and 16 d for each color which are capable of performing color printing. These inkjet head 16 a, 16 b, 16 c, and 16 d are all line heads which extend in the direction of the axis line X1 of the drum 12, and are attached to a frame 16 e, respectively. The inkjet head 16 a, 16 b, 16 c, and 16 d include a plurality of nozzle holes (not shown) for ejecting ink.

An example of the inkjet head 16 a, 16 b, 16 c, and 16 d includes a piezo element as a driving member. The ink is ejected from the nozzle hole when the piezo element is deformed by applying a voltage to the piezo element and the ink is pressurized. In addition, as another example of the driving member, a heating element may be adopted. When the ink is heated using the heating element, the ink is ejected from the nozzle hole due to the pressure of bubble which is generated due to evaporation of ink.

FIG. 2 is a cross-sectional view which shows the inside of the printer 10. The printer 10 has a sheet holding device 50 including the drum 12. Hereinafter, the sheet holding device 50 will be described. The cylinder portion 12 a of the drum 12 includes a plurality of suction holes 51. These suction holes 51 pass through over the inner circumferential surface 12 b and the outer circumferential surface 12 c of the cylinder portion 12 a. The negative pressure chamber 52 is defined in the inside of the drum 12. The suction holes 51 communicate with the negative pressure chamber 52. The drum 12 is supported by the housing 11 using the rotation axis 25, and rotates around the axis line X1. A direction of the axis line X1 is the width direction of the drum 12, that is, the width direction of the endless device.

The air discharging holes 55 are formed at one end portion of the drum 12. The air discharging holes 55 communicate with a duct 56. A suction fan 57 is provided in the duct 56. The suction fan 57 is rotated using a motor 57 a. When the suction fan 57 is rotated, and the air in the negative pressure chamber 52 is discharged to the outside from the duct 56, a negative pressure which is lower than the atmospheric pressure is generated in the negative pressure chamber 52. The suction holes 51, the negative pressure chamber 52, the air discharging holes 55, the suction fan 57, the duct 56, and the like form a suction mechanism 60 which uses a negative pressure.

FIGS. 3A, 3B, and 3C are respective expanded views of the circumferential surface 12 c of the drum 12 according to the embodiment. FIG. 3A shows two sheets S₁ of a first size (for example, A4 size). FIG. 3B shows one sheet S₁ of the first size (for example, A4 size). FIG. 3C shows two sheets S₂ of a second size (for example, the size of a postcard).

These sheets S₁ and S₂ respectively have a pair of long sides which are parallel to each other and a pair of short sides which form right angles (90°) with respect to the long sides. Here, a state where the long side of the sheet goes along the axis line X1 of the drum 12 is referred to as a crosswise position, and a state where the short side of the sheet goes along the axis line X1 of the drum 12 is referred to as a lengthwise position. FIG. 3A shows the first size sheets S₁ in the crosswise position, FIG. 3B shows the first size sheet S₁ in the lengthwise position, and FIG. 3C shows the second size sheets S₂ in the lengthwise position.

As shown in FIGS. 3A, 3B, and 3C, hole rows 51A to 51G which are formed of a plurality of suction holes 51, are formed on the cylinder portion 12 a of the drum 12. These hole rows 51A to 51G are formed of the plurality of suction holes 51 which is formed at intervals in the direction of axis line X1 of the drum 12. These hole rows 51A to 51G are formed in a position which corresponds to the leading end or the trailing end of the sheets S₁ and S₂ in the movement direction. Here, the “leading end” of the sheet is an end which is positioned at the front side in the rotation direction of the drum 12, that is, the front side of the sheet S in the movement direction, and the “trailing end” of the sheet is an end which is positioned at the rear side in the rotation direction of the drum 12, that is, the rear side of the sheet S in the movement direction. A sensor 65 (shown in FIG. 1) which detects the size of the sheet is provided in the sheet conveying path 31.

The first hole row 51A is present in a position which corresponds to the leading end of the sheets S₁ and S₂, so as to adsorb the leading end of the sheets S₁ and S₂ of each size. As shown in FIG. 3C, the second hole row 51B is present in a position which corresponds to the trailing end of the small sheet S₂ of the lengthwise position. As shown in FIG. 3A, the third hole row 51C is present in a position which corresponds to the trailing end of the sheet of S₁ of the crosswise position. As shown in FIG. 3B, the fourth hole row 51D is present in a position which corresponds to the trailing end of the sheet S₁ of the lengthwise position. As shown in FIGS. 3A and 3C, the fifth row hole 51E is present in a position which corresponds to the leading end of the second sheets S₁ and S₂. As shown in FIG. 3C, the sixth hole row 51F is present in a position which corresponds to the trailing end of the second small sheet S₂ of the lengthwise position. As shown in FIG. 3A, the seventh hole row 51G is present on the position which corresponds to the trailing end of the second sheet S₁ of the crosswise position. Since the position and number of these hole rows is set according to a specification of the printer 10, it is needless to say that the hole rows are not limited to the hole rows 51A to 51G which are shown in FIGS. 3A to 3C.

The printer 10 includes an opening and closing mechanism 70 which opens and closes the hole rows 51B to 51G. The opening and closing mechanism 70 includes a plurality of switching blade 71 which is provided in each hole row 51B to 51G. These switching blades 71 are extending in the direction of the axis line X1, along the inner circumferential surface 12 b of the cylinder portion 12 a of the drum 12. The first hole row 51A which is positioned at the foremost in the movement direction, is covered by the leading end of the sheets S₁ and S₂ of each size, therefore, it is possible to omit the switching blade 71. However, the switching blade 71 may be provided to the hole row 51A.

Since all of the switching blades 71 are provided in the cylinder portion 12 a of the drum 12, the switching blades move around the axis line X1 along with the drum 12. In addition, the switching blades 71 are able to slide in the axis line X1 direction of the drum 12, respectively. These switching blades 71 move to a first position (a closing position) shown in FIG. 4 and a second position (an open position) shown in FIG. 5. In the switching blade 71, through holes 72 are formed at positions which correspond to the suction holes 51 of each row hole 51A to 51G, respectively. When the switching blade 71 moves to the first position (shown in FIG. 4), since the positions of the suction holes 51 and the through holes 72 are deviated from each other, the negative pressure chamber 52 is closed. When the switching blade 71 moves to the second position (shown in FIG. 5), since the positions of the suction holes 51 and the through holes 72 match each other, the negative pressure chamber 52 and the outside (the atmospheric side) of the drum 12 communicate with each other.

The switching blade 71 moves in the direction shown by an arrow M1 shown in FIG. 4 and the direction shown by an arrow M2 shown in FIG. 5, along the axis line X1 of the drum 12, using the driving mechanism 75. The driving mechanism 75 is attached to a member on the stationary side (for example, a frame of the housing 11) with respect to the rotating drum 12. The driving mechanism 75 includes, for example, an actuator 76 which is formed of an electric motor, a driving member 78 which includes a driving unit 77 which is driven using the actuator 76, and a power transmission unit 79 which uses, for example, a rack and pinion. The driving unit 77 can be engaged with an engaging portion 71 a of the switching blade 71, when the switching blade 71 of each hole row 51B to 51G moves to a position which corresponds to the driving unit 77 by the rotation of the drum 12. It is possible to use a solenoid in the actuator 76. The power transmission unit 79 may adopt a suitable power transmission member if necessary, such as a chain and sprocket, a wire and pulley, or a combination of spur gears, or the like. The switching blade 71 moves to the drum 12 in the direction of the axis line X1. For this reason, the driving mechanism 75 can move the switching blade 71 between one side in the longitudinal direction and the first and second positions. In addition, the driving mechanism 75 may be disposed at the drum 12. In such a case, the driving mechanism 75 rotates along with the drum 12.

FIG. 6 is a block diagram which shows a configuration of the controller 20 of the printer 10 according to the embodiment. The controller 20 includes a CPU (Central Processing Unit) 80 which functions as a processor. In the CPU 80, a ROM (Read Only Memory) 82, a RAM (Random Access Memory) 83, a communication interface unit 84, a neutralizing and separating controller 85, a discharging roller controller 86, a cleaner driver 87, a sensor input and output port 88, a conveying roller motor driver 90, a drum rotation motor driver 91, a discharge roller motor driver 92, a opening and closing mechanism driver 93, a inkjet head controller 94, a suction fan motor driver 95, a display and operation controller 96, and the like, are connected through a bus line 81.

A program or a variety of persistent data which controls the CPU 80 is stored in the ROM 82. In the RAM 83, various memory areas are formed for storing a variety of data which is necessary for forming images. The communication interface unit 84 controls a data communication which is performed with an external device, through the communication line. The neutralizing and separating controller 85 controls the separation member 35 and the neutralizing charger 17. The charging roller controller 86 controls a DC voltage which is supplied to the charging roller 15. The cleaner driver 87 drives the cleaner 39. Various sensors (for example, a rotation angle sensor 26 or a sheet size sensor 65) are connected to a sensor input and output port 88.

The conveying roller motor driver 90 drives a motor 28 a of the pick-up roller 28, a motor 29 a of the sheet feeding roller 29, and a motor 32 a of the pair of resist rollers 32. The drum rotation motor driver 91 drives a motor 22 which rotates the drum 12. The sheet discharge roller motor driver 92 drives a motor 37 a which rotates the sheet discharge roller 37. The opening and closing mechanism driver 93 drives the actuator 76 of the opening and closing mechanism driver 70. The inkjet controller 94 controls an ink ejection operation of the inkjet head 16 a, 16 b, 16 c, and 16 d. The suction fan motor driver 95 drives a motor 57 a of the suction fan 57. The display and operation controller 96 controls a display device 19 a and an operation unit 19 having a touch panel. It is possible to store information which is necessary for image forming, and information such as the size of the sheet, the direction of the sheet (crosswise position, lengthwise position), or the like, in the RAM 83 by operating the operation unit 19.

Hereinafter, actions of image forming process using the printer 10 according to the embodiment will be described with reference to a flowchart in FIG. 7. In Act 1 in FIG. 7, information on the size of the sheet is obtained. It is possible to manually input by operating the operation unit 19 to obtain size information on the sheet. The size or direction of the sheet (crosswise position, lengthwise position) may be detected using the sheet size sensor 65. Further, information on the number of pages to be printed is obtained in Act 2.

In Act 3 in FIG. 7, the drum 12 is temporarily rotated at a low speed, and the switching blade 71 is moved according to the size of the sheet. The initial position (its original position) of the switching blade 71 is the first position (the closing position) shown in FIG. 4. Among each hole row 51B to 51G, the switching blade 71 which corresponds to a trailing end of the sheet is moved to the second position (the open position) shown in FIG. 5, using the opening and closing mechanism 70, according to the size of the sheet. As shown in FIG. 3A or FIG. 3C, when holding two sheets, the switching blade 71 of the hole row 51E which corresponds to the leading end of the second sheet is moved to the second position (the open position), as well. The lower pressure (the negative pressure) than the atmospheric pressure is generated in the negative pressure chamber 52, since the air in the negative pressure chamber 52 is discharged to the outside from the duct 56 due to rotation of the suction fan 57. Due to this, the leading end and the trailing end of the sheet are ready to be adsorbed to the drum 12.

In this Act 3, it is possible to open in advance the suction hole 51 which is present in a position corresponding to the size of the sheet, by operating the opening and closing mechanism 70, before forming images on the sheet S. For this reason, it is possible to prevent a shock from occurring when forming images using the recording head unit 16.

In Act 4 in FIG. 7, the rotation of the drum 12 returns to its original speed, and the drum 12 rotates at a high speed. In Act 5, the DC voltage is applied to the charging roller 15 by a DC power circuit 34. In Act 6, the sheet S is supplied between the circumferential surface 12 c of the drum 12 and the charging roller 15. That is, the sheet S which is received in the sheet receiving unit 13 is conveyed to a nip between the circumferential surface 12 c of the drum 12 and the charging roller 15, using a supply mechanism 14. The controller 20 controls the operation time, or the like, of the supply mechanism 14, so that the leading end of the sheet S which is conveyed using the supply mechanism 14 is positioned on the first hole row 51A of the rotating drum 12. The sheet S is charged with a charge of a first polarity, and the dielectric layer 27 of the drum 12 is charged with a charge of a second polarity.

In Act 7, the leading end and the trailing end of the sheet S are adsorbed to the circumferential surface 12 c of the drum 12, due to the negative pressure of the suction hole 51. In addition, the sheet S is electrostatically adsorbed to the drum 12. For this reason, the sheet S which is supplied to the circumferential surface 12 c of the drum 12 moves to a rotation direction R1 of the drum 12 along with the drum 12, without separating from the circumferential surface 12 c of the drum 12.

In Act 8 in FIG. 7, the printing is started. In a case of color printing, when the sheet S reaches the first inkjet head 16 a, the first color ink is ejected to the sheet S from the first inkjet head 16 a. The sheet S rotates while being adsorbed to the drum 12, and reaches the second inkjet head 16 b. By doing this, the second color ink is ejected to the sheet S from the second inkjet head 16 b. Further, when the drum 12 rotates, the third color ink is ejected to the sheet S from the third inkjet head 16 c. In addition, when the drum 12 rotates, the fourth color ink is ejected to the sheet S from the fourth inkjet head 16 d. In this manner, an image is formed on the sheet S during the rotation of the drum 12. That is, the printer 10 performs color printing using a multi-path process of a line head-type.

When the printing operation ends in Act 9, an AC voltage is applied to the sheet S on which the image is formed using the recording head unit 16, using the neutralizing charger 17. By doing this, an adsorption force of the sheet S with respect to the drum 12 is weakened. The sheet S is separated from the drum 12 using the separation member 35, and is discharged onto the sheet discharge tray 38 through a conveying guide 36 and the sheet discharge roller 37.

In Act 10 in FIG. 7, it is determined whether or not the subsequent sheet is present, using the sensor which detects the presence of the sheet, or by information on the number of sheets to be printed which is input to the controller 20. If there is no subsequent sheet, the process ends. If there is a subsequent sheet, the process returns to Act 5 again, and printing for the subsequent sheet is performed.

According to the sheet holding device 50 of the embodiment, the leading end and trailing end of the sheet S which are easily separated from the drum 12 are adsorbed to the circumferential surface 12 c of the drum 12, due to the negative pressure of the suction holes 51, in addition to the fact that the entire sheet S is adsorbed to the circumferential surface 12 c of the drum 12 due to the electrostatic adsorption force. In addition, among each suction hole 51, at least a part of the suction hole 51 which is not covered by the sheet S, is closed by the switching blade 71. In this manner, the air is prevented from being sucked into the negative pressure chamber 52, and the negative pressure is not decreased. For this reason, it is possible to reliably hold the sheet S to the circumferential surface 12 c of the drum 12, even when the circumferential surface 12 c which has a curvature like the cylinder portion 12 a of the drum 12 rotates at a high speed. If the sheet S becomes wet due to the ink which is ejected to the sheet S from the recording head unit 16, a bending stress occurs in the sheet S. Even such a sheet S can be reliably held on the circumferential surface 12 c of the drum 12. For this reason, since the drum 12 rotates while reliably attaching the sheet S thereon, it is possible to form images with high quality at a high speed, and prevent paper jamming.

FIGS. 8A to 8C are expanded views which show a cylinder portion 12 a of a drum 12 of a sheet holding device 50′ according to a second embodiment, and correspond to the first embodiment (FIGS. 3A to 3C). The sheet holding device 50′ according to the embodiment also includes a suction mechanism 60 and an opening and closing mechanism 70, similarly to the first embodiment. The sheet holding device 50′ is configured to adsorb a sheet to the drum 12 only using a negative pressure without performing electrostatic adsorption. Intermediate suction holes 99 which is adsorbed between the leading end and the trailing end of the sheet are formed in the cylinder portion 12 a of the drum 12, in addition to hole rows 51A to 51G which are the same as those in the first embodiment. These intermediate suction holes 99 communicate with the negative pressure chamber 52. The intermediate suction holes 99 are smaller than the suction holes 51 which form the hole rows 51A to 51G. For this reason, even if the switching blade 71 is not provided in the intermediate suction holes 99, it is possible to prevent air from being sucked to the negative pressure chamber 52 from the outside of the drum 12. In addition, it may be possible to open and close the intermediate suction holes 99, by providing the switching blade 71 in the intermediate suction holes 99.

In the second embodiment, since the sheet is held to the drum 12 only using the adsorption force due to the negative pressure, it is not necessary to provide the dielectric layer or the charging roller, and the DC power circuit of the first embodiment. Accordingly, it is advantageous that the structure can be simplified compared to a case where the electrostatic adsorption is used together. The other configurations and operation of the sheet holding device 50′ are common to the sheet holding device 50 in the first embodiment, and will be denoted by the same reference numerals, and a description thereof will be omitted.

FIG. 9 shows an inkjet printer 10A according to a third embodiment. This inkjet printer 10A has a belt 100 as an example of an endless device. The belt 100 of the sheet holding device is stretched across a first rotation body 101 and a second rotation body 102, and performs an endless rotation movement (a circulation movement) in the direction of an arrow R2 using a driving mechanism (not shown). A recording head unit 16 including inkjet heads 16 a, 16 b, 16 c, and 16 d, is disposed in the movement direction of the belt 100. The sheet S, which is supplied by a supply mechanism 103, is supplied between the belt 100 and a charging roller 105 through a conveying path 104. The charging roller 105 applies a charge for electrostatic adsorption to a dielectric layer which is provided on a circumferential surface of the belt 100. An image is formed on the sheet S using the inkjet heads 16 a, 16 b, 16 c, and 16 d when the sheet S is conveyed by the belt 100 in the direction shown by an arrow M3. The sheet S on which the image is formed is discharged from a sheet conveying mechanism 106. A negative pressure chamber 52 is defined in the inside of the belt 100. A negative pressure is generated in the negative pressure chamber 52, when air in the negative pressure chamber 52 is discharged using the suction mechanism.

Hole rows which are formed of suction holes are formed in the belt 100 in a position which corresponds to at least the leading end and the trailing end of the sheet S. These suction holes communicate with the negative pressure chamber 52. In addition, the switching blade 71 is provided in the belt 100. The the switching blade 71 opens and closes the suction holes. A support member 110 is provided in the vicinity of the recording head unit 16 of the belt 100, in order to prevent the belt 100 from bending due to the negative pressure. The switching blade 71 can move to a first position which closes suction holes and a second position which opens the suction holes, using a driving mechanism 75. The other configuration and operation of the printer 10A are common to the printer 10 in the first embodiment, they will be denoted by the same reference numeral, and a description thereof will be omitted.

As described above, in the printer according to each of the embodiments, sheets are adsorbed to the circumferential surface of the endless device before forming the image, by opening and closing suction holes in a position which corresponds to the size of the sheet, using an switching blade. For this reason, an image forming operation is not affected due to a vibration, and it is possible to promptly move to the image forming operation with respect to a recording medium which is supplied to the endless device. In addition, since at least a part of the suction holes which are not contributing to the adsorption of the sheet, are shut using the switching blade, it is possible to suppress suction of the air into the negative pressure chamber, and maintain the adsorption force of the sheet. The embodiment can be applied to a thermal printer or a wire dot printer, in addition to the inkjet printer.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. A holding device of a recording medium comprising: an endless device which includes a circumferential surface which holds the recording medium, a plurality of suction holes which is formed on the circumferential surface, and a negative pressure chamber which communicates with the suction holes, and rotates in a predetermined direction; a suction mechanism which discharges air in the negative pressure chamber; a switching blade which is provided in the endless device, and moves between a first position at which the suction holes are closed and a second position at which the suction holes are opened; and a driving mechanism which moves the switching blade to the first position and the second position.
 2. The device according to claim 1, wherein the endless device includes the front side hole row which is formed such that a plurality of the suction holes is formed to have a interval in a width direction of the endless device, in a position which corresponds to a leading end of the recording medium in a movement direction, which is held by the endless device.
 3. The device according to claim 2, wherein the endless device includes the rear side hole row which is formed such that a plurality of the suction holes is formed to have a internal in a width direction of the endless device, in a position which corresponds to a trailing end of the recording medium in a movement direction, which is held by the endless device.
 4. The device according to claim 2, wherein the endless device includes a first rear side hole row which is formed such that a plurality of the suction holes is formed in a position which corresponds to a trailing end of the recording medium of a first size, in a movement direction, and a second rear side hole row which is formed such that a plurality of the suction holes is formed in a position which corresponds to a trailing end of the recording medium of a second size in the movement direction.
 5. The device according to claim 4, wherein the front side hole row is always open, and the switching blade is disposed at the first and second rear side hole rows.
 6. The device according to claim 1, wherein the endless device is a drum, and the switching blade moves in an axial direction of the drum.
 7. The device according to claim 6 comprising: an engaging portion in which the switching blade extends in the axial direction of the drum, wherein the driving mechanism includes a driving member which has the driving unit engaging with the engaging portion, and an actuator which moves the switching blade to the first position and the second position if the engaging portion and the driving unit engage with each other.
 8. The device according to claim 1, wherein a dielectric layer to which a charge for electrostatically adsorbing the recording medium is applied is provided on the circumferential surface of the endless device.
 9. The device according to claim 3, wherein the endless device further includes a plurality of intermediate suction holes which communicates with the negative pressure chamber between the front side hole row and the rear side hole row.
 10. The device according to claim 9, wherein the intermediate suction holes are smaller than those of the front and rear side hole rows.
 11. An image forming apparatus comprising: an endless device which includes a circumferential surface which holds the recording medium, a plurality of suction holes which is formed on the circumferential surface, and a negative pressure chamber which communicates with the suction holes; a rotation mechanism which rotates the endless device in a predetermined direction; a suction mechanism which discharges air in the negative pressure chamber; a opening and closing mechanism which has a switching blade which is provided in the endless device, and moves between a first position at which the suction holes are closed and a second position at which the suction holes are opened; a driving mechanism which moves the switching blade to the first position and the second position; a recording head unit which is arranged to face a circumferential surface of the endless device, and forms images on the recording medium; a supplying mechanism which supplies the recording medium to the circumferential surface of the endless device; and a controller which drives the opening and closing mechanism according to a size of the recording medium.
 12. The apparatus according to claim 11, wherein the endless device includes hole rows which are formed such that the plurality of suction holes is formed to have a interval in a width direction of the endless device, and wherein the controller controls the supply mechanism so that the leading end of the recording medium which is supplied to the endless device is positioned on the hole rows.
 13. The apparatus according to claim 11 further comprising: a dielectric layer which is provided on the circumferential surface of the endless device, and to which a charge for electrostatically adsorbing the recording medium, is applied; a charging roller which applies the charge to the dielectric layer; and a neutralizing charger which neutralizes the charge from the recording medium on which the image is formed.
 14. The apparatus according to claim 11, wherein the endless device is a drum, and the switching blade moves in the axial direction of the drum.
 15. The apparatus according to claim 11, wherein the endless device includes the front side hole row which is formed in a position which corresponds to the leading end of the recording medium in a movement direction which is held to the endless device; the rear side hole row which is formed in a position which corresponds to the trailing end of the recording medium in the movement direction; and a plurality of intermediate suction holes which communicates with the negative pressure chamber and which is formed between the front side hole row and the rear side hole row.
 16. The apparatus according to claim 15, wherein the intermediate suction holes are smaller than those of the front side hole row and the rear side hole row.
 17. A conveying method of a recording medium comprising: generating a negative pressure in a negative pressure chamber of an endless device including a plurality of suction holes on a circumferential surface; opening suction holes in a position which corresponds to a size of the recording medium, among the plurality of suction holes; closing at least a part of the suction holes in a position which is not covered by the recording medium, among, the plurality of suction holes; adsorbing the recording medium to the circumferential surface of the endless device, by allowing the negative pressure to act on the recording medium through the opened suction holes; and conveying the recording medium to the recording head unit by rotating the endless device.
 18. The method according to claim 17, wherein the recording medium is supplied to the circumferential surface of the endless device such that the leading end and the trailing end are supposed to position at the opened suction holes.
 19. The method according to claim 17, wherein a charge is applied to the circumferential surface of the endless device, in order to electrostatically adsorb the recording medium, using the charge, and wherein the recording medium is adsorbed in the electrostatic manner to the circumferential surface of the endless device, and the leading end and the trailing end of the recording medium are adsorbed to the endless device using the negative pressure.
 20. The method according to claim 17, wherein the leading end and the trailing end of the recording medium in the movement direction, are adsorbed to the endless device using the negative pressure which acts through the suction holes, and portions between the leading end and the trailing end of the recording medium are adsorbed to the endless device using the negative pressure which acts through suction holes smaller than the above suction holes. 